1. Wuhan National Laboratory for Optoelectronics (WNLO) and School of Optical and Electronic Information; Huazhong University of Science and Technology; Wuhan 430074 China
2. Materials Research Center for Element Strategy; Tokyo Institute of Technology; Yokohama 226-8503 Japan
3. Laboratory for Materials and Structures; Tokyo Institute of Technology; Yokohama 226-8503 Japan
4. Schulich Faculty of Chemistry; Russell Berrie Nanotechnology Institute; Solid State Institute; Technion Haifa 32000 Israel
5. ARC Centre of Excellence in Exciton Science; Department of Materials Science and Engineering; Monash University; Clayton Victoria 3800 Australia